Chemical vapor deposition (CVD) is a process used to deposit semiconductor, dielectric, metallic and other thin films onto a surface of a substrate. In one common CVD technique, one or more precursor molecules, each in a gas phase, are introduced into a process chamber that includes the substrate. The reaction of these precursor gases at the surface of the substrate is initiated or enhanced by adding energy. For example, energy can be added by increasing the surface temperature or by exposing the surface to a plasma discharge or ultraviolet (UV) radiation source.
The quality of a film deposited by a CVD reaction occurring in the gas phase depends significantly on the uniformity of the precursor gas flows. Non-uniform gas flow near the substrate surface can yield unsatisfactory film uniformity and can lead to shadowing artifacts due to features on the surface, such as steps and vias. High volume processing of wafers and other discrete substrates, and high speed processing of web substrates in roll-to-roll deposition systems are limited by known systems and methods for CVD processing, and are often costly to operate based on material utilization and other factors.
Atomic layer deposition (ALD) is another technique in which a film is deposited onto a surface of a substrate. According to the ALD process, a first precursor gas flow is used to react with the surface to generate a monolayer. The first precursor gas flow is terminated and a second precursor gas flow is then used to generate another monolayer. This two-step sequence of “pulsing” precursor gases is repeated a number of times until a thin film of a single material at a desired thickness is achieved. In other versions of the ALD process, more than two precursor gas flows are used in sequence to generate the thin film. The introduction of each precursor gas to the reaction chamber may be preceded by the introduction of a purge gas to ensure that the previous precursor gas has been removed, thereby reducing or preventing unwanted deposition byproducts. Although providing excellent thickness control, the ALD process of producing alternating monolayers on the surface of the substrate is time intensive and significantly limits throughput.